Child protected by vaccines

Childhood Vaccines: Separating Fact from Fiction about Non-Specific Effects

Jordan Keane in Health & Wellness June 2025 • 4 min read.

"Are some vaccines doing more than we thought? Let's explore the evidence, biases, and what the experts really say."

Vaccines are designed to protect us from specific diseases, but what if they have other effects, both good and bad? These 'non-specific effects' have been a topic of much discussion. But figuring out what's real and what's just a coincidence is tricky.

Two new systematic reviews took a close look at the evidence on these non-specific effects from common childhood vaccines like BCG, DPT, and measles vaccines (MCV). They wanted to help the World Health Organization (WHO) decide if any changes were needed in how these vaccines are used.

It's super important to know that these reviews weren't questioning whether vaccines are safe or if kids should still get them. These vaccines save lives! The goal was to see if there were any unexpected extra benefits or risks we should know about.

Unpacking the Research: What Did They Really Find?

The first review looked at studies on how BCG, DPT, and MCV vaccines affected overall mortality (death rates) in kids under 5. The researchers were careful to only include studies that weren't likely to be too biased. It's easy to make mistakes when studying vaccines because kids who are already sick are less likely to get vaccinated.

One controversial finding was that the DPT vaccine might be linked to higher death rates in some studies. However, all these studies had a high risk of bias, so we can't really trust that result. On the other hand, some randomized trials suggested that the BCG vaccine might actually reduce overall mortality.

BCG Vaccine: Showed potential to reduce overall mortality in randomized trials.
DPT Vaccine: Linked to higher death rates in biased studies, results are questionable.
MCV Vaccine: Suggested a possible protective effect against mortality, especially for girls.

The second review looked at how these vaccines affected the immune system. The problem is, we don't really know which immune markers would tell us for sure if there are clinically important non-specific effects. The review did find some trends, like increased levels of a certain immune marker (IFN-γ) in people who got the BCG vaccine. Measles vaccines were also linked to immune responses to other antigens. But what this all means for real-world health is still unclear.

The Bottom Line: What Does This Mean for You?

Both reviews suggest that vaccines might have non-specific effects, but the evidence is still weak. The WHO's expert group decided that we don't need to change current vaccination schedules. More small, biased studies won't help us get closer to the truth. We need better, more innovative studies to really understand what's going on.

About this Article -

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Everything You Need To Know

What are non-specific effects of childhood vaccines, and why is there so much discussion around them?

Non-specific effects refer to the potential impacts that vaccines, like BCG, DPT, and measles vaccines (MCV), might have beyond protecting against the specific diseases they are designed for. These effects can be either beneficial or detrimental. The discussion arises because understanding these effects could lead to optimizing vaccination schedules or identifying unexpected benefits or risks. It's important to remember that exploring these effects does not question the safety or necessity of vaccines themselves.

How did the systematic reviews evaluate the non-specific effects of BCG, DPT, and measles vaccines (MCV)?

The systematic reviews focused on two main aspects: the impact of BCG, DPT, and measles vaccines (MCV) on overall mortality (death rates) in children under 5, and their effects on the immune system. The mortality review looked for unbiased studies to determine if the vaccines were linked to changes in death rates. The immune system review examined various immune markers to see if there were consistent changes after vaccination. However, it's challenging to interpret these immune markers without knowing which ones are clinically significant.

What were the controversial findings regarding the DPT vaccine, and why should they be interpreted with caution?

Some studies suggested a link between the DPT vaccine and higher death rates. However, these studies were identified as having a high risk of bias. This means that the results might be skewed due to factors not properly controlled, such as pre-existing health conditions in the children studied. Therefore, this potential link should be interpreted cautiously and not be taken as definitive evidence of harm.

What potential benefits were observed with the BCG and measles vaccines (MCV) in relation to non-specific effects?

The BCG vaccine showed potential in reducing overall mortality based on randomized trials. This suggests it might offer protection beyond just tuberculosis. Measles vaccines (MCV) also suggested a possible protective effect against mortality, particularly for girls. These findings are considered preliminary, and further research is needed to confirm these benefits and understand the mechanisms behind them.

Given the uncertainty around non-specific effects, what kind of research is needed to better understand the potential benefits and risks of vaccines like BCG, DPT, and measles vaccines (MCV)?

The consensus is that more rigorous and innovative studies are needed. Small, biased studies won't provide reliable answers. Future research should focus on well-designed, large-scale studies that minimize bias and can accurately assess the impact of these vaccines on both specific disease protection and overall health outcomes. Specifically more research is needed to understand which immune markers would definitively indicate clinically important non-specific effects.